Ventilation Control Measures
Strategy & Controls · Strategy & Controls overview
Ventilation control measures are the engineered and procedural arrangements that use airflow to reduce worker exposure to airborne contaminants. Under COSHH they sit within the hierarchy of control as the principal engineering response when elimination, substitution and enclosure cannot fully eliminate the risk.
What ventilation control measures are
A ventilation control measure is any deliberate use of air movement to limit exposure. That includes local exhaust ventilation hoods and booths, partial and total enclosures with integrated extract, dilution and general ventilation, segregation of clean and dirty zones using pressure differentials, controlled make-up air, and the maintenance and user practices that keep all of the above working as designed.
The control is not the equipment alone — it is the whole arrangement, including how it is used. A correctly specified LEV hood used 300 mm away from the source delivers a fraction of its designed protection. Control measure thinking treats engineering and behaviour as a single system.
Where ventilation fits in the hierarchy of control
The COSHH hierarchy ranks controls by reliability: eliminate the substance, substitute with something less hazardous, enclose the process, control with engineering (including ventilation), reduce exposure with systems of work, and finally protect the individual with personal protective equipment. Ventilation sits firmly in the engineering tier and outranks PPE because it does not depend on individual user behaviour to deliver protection.
Within ventilation itself there is a hierarchy too. Total enclosure with extract is the strongest; partial enclosure with capture is next; receiving hoods and captor hoods follow; and general dilution sits at the weakest end. The right choice depends on the contaminant, the process and the practicality of the work.
The main ventilation control measures
Most UK workplaces use a combination of the following, layered to suit the process.
- Source capture (LEV) — extract at or as close as practicable to the point of release.
- Enclosure — physical containment around the process, often combined with extract to maintain inward airflow.
- Dilution and general ventilation — fresh air supply and extract to reduce residual concentrations across the space.
- Segregation — separating contaminated and clean zones, typically with pressure differentials and controlled transfer routes.
- Make-up air — engineered replacement of extracted air, sized and tempered so extraction systems can operate at design volume.
- Maintenance and user practice — cleaning, filter management, hood positioning, work method and training that keep controls effective.
How control measures are selected and reviewed
Selection starts with the substance and the process. Toxicity, form (dust, fume, vapour, mist), release rate, work method and the proximity of the breathing zone all influence which controls are reasonably practicable. The risk assessment under COSHH documents the choice and the rationale.
Review is continuous, not one-off. Statutory LEV thorough examination at least every 14 months is the minimum baseline; controls should also be reviewed whenever the process, substance, layout or workforce changes, and whenever exposure monitoring, health surveillance or worker reports suggest the existing arrangement is no longer adequate.
Why controls fail in real workplaces
Failures are rarely the result of the engineering itself being wrong from day one. They develop over time and through use.
- Hoods relocated or removed because they obstruct the work.
- Filters loaded, fans worn or ducts partially blocked, reducing volume below design.
- Process changes — different substances, faster cycles, additional sources — that the original control was never sized for.
- Insufficient make-up air, depressurising the building and starving extract fans.
- Operator practice that defeats the control, such as standing between the source and the hood.
- No documented maintenance regime, so degradation is invisible until something fails.
Supporting COSHH risk management and improvement planning
Ventilation control measure findings feed directly into the COSHH risk assessment and into the wider improvement plan. A structured assessment identifies which controls are adequate, which need adjustment, and which require redesign or replacement. Recommendations are prioritised by exposure reduction rather than by ease of capital approval.
This evidence base is what employers rely on in front of HSE inspectors, insurers and clients. It also gives senior management a defensible basis for capital allocation, replacing anecdote with measured performance against the substances and processes actually in use.
Frequently asked questions
Is LEV the only acceptable ventilation control measure?
No. LEV is the strongest engineered control for point sources, but enclosure, segregation, dilution and make-up air are all legitimate controls when matched to the substance and process. The COSHH risk assessment should justify the combination chosen.
How does ventilation relate to PPE?
Respiratory PPE sits below engineering controls in the hierarchy because it depends on correct use by each individual every time. Ventilation controls protect the workforce by default and should be specified before reliance on PPE.
How often should control measures be reviewed?
LEV requires thorough examination and test at least every 14 months. Wider ventilation control measures should be reviewed whenever process, substance, layout or workforce change, and in response to exposure data, health surveillance findings or worker reports.
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